Extreme ultraviolet light generation apparatus

ABSTRACT

An extreme ultraviolet light generation apparatus may include: a laser apparatus; a chamber provided with an inlet for introducing a laser beam outputted from the laser apparatus to the inside thereof; a target supply unit provided to the chamber for supplying a target material to a predetermined region inside the chamber; a collector mirror disposed in the chamber for collecting extreme ultraviolet light generated when the target material is irradiated with the laser beam in the chamber; an extreme ultraviolet light detection unit for detecting energy of the extreme ultraviolet light; and an energy control unit for controlling energy of the extreme ultraviolet light.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority from Japanese Patent ApplicationNo. 2010-055153 filed Mar. 11, 2010, and Japanese Patent Application No.2011-018748 filed Jan. 31, 2011, the disclosure of each of which isincorporated herein by reference in its entirety.

BACKGROUND

1. Technical Field

This disclosure relates to an apparatus for generating extremeultraviolet (EUV) light.

2. Related Art

With recent increase in integration of semiconductor process, transferpatterns for use in photolithography of the semiconductor process haverapidly become finer. In the next generation, microfabrication at 70 to45 nm, and further, microfabrication at 32 nm or less is to be demanded.Accordingly, for example, to meet the demand for microfabrication at 32nm or less, an exposure apparatus is expected to be developed, where EUVlight of a wavelength of approximately 13 nm is combined with areduction projection reflective optical system.

There are mainly three types of known EUV light generation apparatuses,namely, a laser produced plasma (LPP) type apparatus using plasmaproduced as a target material is irradiated with a laser beam, adischarge produced plasma (DPP) type apparatus using plasma produced bydischarge, and a synchrotron radiation (SR) type apparatus using orbitalradiation.

SUMMARY

An extreme ultraviolet light generation apparatus according to oneaspect of this disclosure may include: a laser apparatus; a chamberprovided with an inlet for introducing a laser beam outputted from thelaser apparatus to the inside thereof; a target supply unit provided tothe chamber for supplying a target material to a predetermined regioninside the chamber; a collector mirror disposed in the chamber forcollecting extreme ultraviolet light generated when the target materialis irradiated with the laser beam in the chamber; an extreme ultravioletlight detection unit for detecting energy of the extreme ultravioletlight; and an energy control unit for controlling energy of the extremeultraviolet light.

According to another aspect of this disclosure, a method for controllingan output of burst-outputted extreme ultraviolet light, in an extremeultraviolet light generation apparatus including a laser apparatus, achamber, a target supply unit, a collector mirror for collecting extremeultraviolet light, an extreme ultraviolet light detection unit, and anenergy control unit for controlling energy of the extreme ultravioletlight, may include: supplying a target material into the chamber;irradiating the target material with a laser beam; detecting energy ofan extreme ultraviolet light pulse emitted when the target material isirradiated with the laser beam; and controlling energy of an extremeultraviolet light pulse outputted following the extreme ultravioletlight pulse, based on the detection result.

These and other objects, features, aspects, and advantages of thisdisclosure will become apparent to those skilled in the art from thefollowing detailed description, which, taken in conjunction with theannexed drawings, discloses preferred embodiments of this disclosure.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 schematically illustrates an EUV light generation systemaccording to a first embodiment of this disclosure.

FIG. 2 illustrates change over time in ideal EUV pulse energy atsuccessive burst light emission.

FIG. 3 illustrates change over time in EUV pulse energy when feedbackcontrol is not performed at burst light emission.

FIG. 4 is a flowchart showing overall control procedure including energycontrol processing by an EUV light generation controller.

FIG. 5 is a flowchart showing the energy control processing procedureshown in FIG. 4.

FIG. 6 is a flowchart showing burst-lead control processing procedureshown in FIG. 5.

FIG. 7 is a flowchart showing feedback control processing procedureshown in FIG. 5.

FIG. 8 schematically shows change over time in signals at successiveburst light emission.

FIG. 9 is a time chart showing, in enlargement, the change over time insignals between two burst light emission shown in FIG. 8.

FIG. 10 is a flowchart showing control amount read-out processingprocedure according to the first embodiment of this disclosure.

FIG. 11 is a flowchart showing control amount update processingprocedure according to the first embodiment of this disclosure.

FIG. 12 shows an example of a relation table according to a secondembodiment of this disclosure.

FIG. 13 is a flowchart showing control amount read-out processingprocedure according to a third embodiment of this disclosure.

FIG. 14 is a flowchart showing control amount update processingprocedure according to the third embodiment of this disclosure.

FIG. 15 is a flowchart showing control amount read-out processingprocedure according to a fourth embodiment of this disclosure.

FIG. 16 is a flowchart showing control amount update processingprocedure according to the fourth embodiment of this disclosure.

FIG. 17 is a flowchart showing control amount read-out processingprocedure according to a fifth embodiment of this disclosure.

FIG. 18 is a flowchart showing control amount update processingprocedure according to the fifth embodiment of this disclosure.

FIG. 19 is a flowchart showing control amount read-out processingprocedure according to a sixth embodiment of this disclosure.

FIG. 20 is a flowchart showing control amount update processingprocedure according to the sixth embodiment of this disclosure.

FIG. 21 is a flowchart showing control amount read-out processingprocedure according to a seventh embodiment of this disclosure.

FIG. 22 is a flowchart showing control amount update processingprocedure according to the seventh embodiment of this disclosure.

FIG. 23 schematically shows change in signals at successive burst lightemission, in a case where a trigger signal is a signal indicating aburst light emission period.

FIG. 24 is a time chart showing, in enlargement, the change in signalsbetween two burst light emission shown in FIG. 23.

FIG. 25 schematically illustrates a configuration of the EUV lightgeneration system according to a modification of this disclosure.

FIG. 26 schematically illustrates an example of an oscillator shown inFIG. 25.

FIG. 27 schematically illustrates another example of an oscillator shownin FIG. 25.

FIG. 28 schematically illustrates an example of an oscillator shown inFIG. 25, the oscillator being configured of semiconductor lasers.

FIG. 29 schematically illustrates an example of an oscillator shown inFIG. 25, the oscillator being provided with a high-speed shutter on theexterior thereof.

FIG. 30 schematically illustrates another example of an oscillator shownin FIG. 25, the oscillator being provided with a high-speed shutter onthe exterior thereof.

FIG. 31 schematically illustrates an EUV light generation systemaccording to a second modification of this disclosure, in which aregenerative amplifier is provided between an oscillator and apreamplifier.

FIG. 32 shows operation of the regenerative amplifier shown in FIG. 31.

FIG. 33 schematically illustrates a configuration of an EUV lightgeneration system according to a third modification of this disclosure.

FIG. 34 schematically illustrates the EUV light generation systemaccording to the first embodiment, to which a pre-pulse laser isadditionally provided.

DESCRIPTION OF PREFERRED EMBODIMENTS

Hereinafter, embodiments of this disclosure will be described in detailwith reference to the accompanying drawings. The embodiments describedbelow merely show an example of this disclosure and do not limit thescope of this disclosure. Further, configurations and operationdescribed in each embodiment may not be required configurations andoperation of this disclosure. It should be noted that like elements arereferenced by like reference numerals, and duplicate description thereofwill be omitted.

First Embodiment

First, an EUV light generation apparatus according to a first embodimentof this disclosure will be described. FIG. 1 is a schematic diagramillustrating a configuration of an EUV light generation system accordingto the first embodiment. The EUV light generation system may include adriver laser 1, an EUV light generation apparatus 2 for generating EUVlight L2 using CO₂ pulsed laser beam L1 outputted from the driver laser1, and an EUV light source controller C capable of controlling thedriver laser 1 and the EUV light generation apparatus 2.

The driver laser 1 may output the CO₂ pulsed laser beam L1 under thecontrol of the EUV light source controller C. The outputted CO₂ pulsedlaser beam L1 may be reflected by an HR (high reflection) mirror M1 andan off-axis paraboloidal mirror M2, and may enter an EUV chamber 10through a window 15 of the EUV light generation apparatus 2.

In the EUV light generation apparatus 2, a target generator 12 mayoutput a target 13, which is a droplet of Sn, so that the target 13passes through a plasma generation region PL inside the EUV chamber 10.The timing at which the target 13 is outputted from the target generator12 may be controlled with a droplet control signal S4 sent from the EUVlight source controller C to a droplet controller 11. The dropletcontroller 11 may control the timing at which the target 13 is generatedin response to the droplet control signal S4. Among the outputtedtargets 13, targets 13 that have not contributed to the generation ofEUV light may be collected into a target collection unit 14 disposed soas to face the target generator 12. Further, the EUV light generationapparatus 2 may include an EUV light detector 16. The EUV light detector16 may detect the energy of EUV light emitted in the plasma generationregion PL, and may output an EUV pulse energy detection signal S2 to theEUV light source controller C.

Meanwhile, the CO₂ pulsed laser beam L1, outputted from the driver laser1, having entered the EUV chamber 10 may be focused in the plasmageneration region PL through a through-hole provided at the center of anEUV collector mirror M3. In the plasma generation region PL, the target13 may be irradiated with the CO₂ pulsed laser beam L1, whereby thetarget material 13 may be turned into plasma. EUV light L2 with awavelength of approximately 13.5 nm may be emitted from this plasma. Theemitted EUV light L2 may be collected by the EUV collector mirror M3,and focused at an intermediate focus IF. Further, the EUV light L2 mayenter an exposure apparatus 100 while diverging from the intermediatefocus IF.

Based on a trigger signal S1 from the exposure apparatus 100, the EUVlight source controller C may control such that at least the timing atwhich the target 13 is generated is synchronized with the timing atwhich the CO₂ pulsed laser beam L1 is outputted from the driver laser 1,thereby controlling the generation of the EUV light L2 in the plasmageneration region PL.

The EUV light source controller C may perform burst lead controlprocessing so that at least lead-side pulse energy is stably at adesirable value at burst light emission. The EUV light source controllerC may include an energy control processing unit 20, a pulse history unit21, a timer 22, and a control amount storage unit 23. The pulse historyunit 21 may store an EUV pulse energy value within a predetermined timeTw together with a pulse generation time. In this processing of the EUVpulse energy history, a time at which an EUV pulse is generated may beidentified based on the trigger signal S1 from the exposure apparatus100, and an EUV pulse energy value may be identified based on the EUVpulse energy detection signal S2 from the EUV light detector 16. The EUVpulse energy detection signal S2 may, instead of a detection signal fromthe EUV light detector 16, be an EUV pulse energy detection signal froman EUV light detector (not shown) provided to the exposure apparatus100. Alternatively, the configuration may be such that the EUV pulseenergy detection signals from both the exposure apparatus 100 and theEUV light detector 16 are used as the EUV pulse energy detection signalS2. The timer 22 may time a predetermined time, for example, a triggerwait time T, which will be described later. The control amount storageunit 23 may updatably store, as a parameter log, a control amount of thelead-side pulse energy corresponding to an averaged EUV pulse energygenerated within the predetermined time Tw. The energy controlprocessing unit 20 may perform feedback control, and in particular, theenergy control processing unit 20 may learn and update the controlamount of the lead-side pulse energy based on the parameter log storedin the pulse history unit 21. The energy control processing unit 20 mayperform the burst lead control processing for stabilizing an output oflead-side pulse energy, based on the control amount of the updatedlead-side pulse energy.

Here, an ideal burst light emission pattern will be described. FIG. 2 isa time chart showing a case in which burst light emission has beengenerated in order of B11, B12, B13, B14, and B15, and burst lightemission B to be controlled next is to be generated. In this case, theburst light emission B12, B13, B14, and B15 are generated within theabove-mentioned predetermined time Tw. Also, a burst-length time TB maybe a period of the burst light emission B15 immediately preceding theburst light emission B to be controlled. Also, a burst-rest time Tr maybe a light-emission-rest time immediately preceding the burst lightemission B to be controlled. FIG. 2 shows an ideal burst light emission,in which EUV pulse energy Ep is uniform for every burst light emission.

FIG. 3 shows change over time in EUV pulse energy in the case where thefeedback control is not performed for burst light emission. In thisburst light emission, 31 successive EUV pulses P1 through P31 aregenerated, for example. Here, EUV pulses subject to the burst leadcontrol processing by the energy control processing unit 20 may be EUVpulses within a learning control region E1. To be more specific, the EUVpulses subject to the burst lead control processing may be the first mEUV pulses; that is, seven EUV pulses of EUV pulses P1 through P7.Further, EUV pulses within a feedback region E2 may be k EUV pulses ofthe (m+1)-th pulse through the (m+k)-th pulse, which is the last pulse;that is, 24 EUV pulses of EUV pulses P8 through P31. In this feedbackcontrol, the EUV pulse energy of an EUV pulse may be controlled based onthe EUV pulse energy of an immediately preceding EUV pulse within theburst light emission.

In general, an EUV light generation system is used as a light source foran exposure apparatus in which an irradiation object, such as asemiconductor wafer, is exposed to light, and which repeats lightemission operation with step and scan system. In other words, the EUVlight generation apparatus repeats such operation pattern thatsuccessive pulsed light emission, i.e., burst light emission at apredetermined operating frequency is performed during scanning exposureand the pulsed light emission is paused during step movement. In orderto have this operation pattern repeated, burst oscillation operation isperformed, where successive pulse oscillation for a predetermined timein which the burst light emission is performed and pulse oscillationpause are repeated.

Here, when the feedback control is not performed for the EUV pulseenergy at the burst light emission, a burst light emission pattern maybe such that a value of the EUV pulse energy is not constant, as shownin FIG. 3. In particular, with an existing EUV light generation system,each EUV pulse energy is detected at burst light emission, or anaveraged EUV pulse energy within a predetermined period is detected,whereby the feedback control is performed for each EUV pulse energy.

However, as shown in FIG. 3, the value of the lead-side pulse energy ofburst light emission, in particular, the value of lead pulse energytends to be a large value, and in many cases, the energy value mayexceed the range of values which can be controlled with the feedbackcontrol. That is, it is difficult to generate an ideal burst lightemission in which values of the EUV pulse energy in a burst lightemission period are uniform as shown in FIG. 2. It is contemplated thatthis is because a burst rest period is provided between burst lightemission and a thermal condition in the EUV light generation system maychange between the burst light emission period and the burst restperiod. Hence, even if the feedback control is performed, it isdifficult to stably control the lead-side pulse energy to be apredetermined pulse energy value. Further, when the burst light emissionperiod, the burst rest period, and so forth vary, or when a desirablevalue of EUV pulse energy varies for each burst light emission period,it is even more difficult to stably control the value of the lead-sidepulse energy.

In controlling to stabilize the lead-side pulse energy, even if burstoscillation by the driver laser of the EUV light generation system isstabilized, it is highly likely that the EUV pulse energy cannot bestabilized. That is, the change in thermal condition in the EUV lightgeneration system is a thermal change in an optical element such as amirror in the EUV light generation system, and this optical element mayalso be used for the output of the EUV light.

In the first embodiment, in order to control such that the lead-sidepulse energy value at the burst light emission is stabilized at adesirable value, the energy control processing unit 20 is configured toperform the burst lead control processing. In this specification, “burstoutput” is defined as a case in which a successive pulse output of EUVlight for a predetermined time and pulse output pause are alternatelyrepeated.

Next, energy control processing including the burst lead controlprocessing by the energy control processing unit 20 will be describedwith reference to the drawings. FIG. 4 is a flowchart showing theoverall control procedure including the energy control processing by theEUV light source controller C. FIG. 5 is a flowchart showing the energycontrol processing procedure shown in FIG. 4. FIG. 6 is a flowchartshowing the burst lead energy control processing procedure shown in FIG.5. FIG. 7 is a flowchart showing the feedback control processingprocedure shown in FIG. 5. FIG. 8 is a time chart schematically showingchange over time in signals during successive burst light emission. FIG.9 is a time chart showing, in enlargement, change over time in signalsbetween two burst light emission shown in FIG. 8.

First, as shown in FIG. 4, the EUV light source controller C may performinitialization (step S101). This initialization may include setting aninitial value of a trigger wait time T so as to be larger than a burststart threshold Tth, setting an initial value for a control amount to beused in the burst lead control processing, and so forth. Then, the EUVlight source controller C may perform energy control processing forstabilizing each pulse energy value at the burst light emission at adesirable value (step S102). Then, the EUV light source controller C maydetermine whether or not processing for stopping laser oscillation isperformed (step S103). If the laser oscillation is stopped (step S103,Yes), this processing is ended, and if the laser oscillation is notstopped (step S103, No), this processing shifts to step S102, and theenergy control processing may be performed.

As shown in FIG. 5, in the energy control processing in step S102, itmay first be determined whether or not the energy control processingunit 20 has detected the trigger signal S1 inputted from the exposureapparatus 100 (step S111). If the energy control processing unit 20detects the trigger signal S1 (step S111, Yes), it may be determinedwhether or not the trigger wait time T is larger than the burst startthreshold Tth (step S112). As shown in FIG. 9, this trigger wait time Tmay be a time between trigger signals S1, and may be a value set in theinitialization or a time timed by the timer 22. The burst startthreshold Tth may be a predetermined value, and may, for example, be 20ms. As shown in FIG. 9, this burst start threshold Tth may be a valuelarger than an EUV pulse interval Tp in a burst light emission period.

If the trigger wait time T is equal to or larger than the burst startthreshold Tth (step S112, Yes), the energy control processing unit 20may set a burst pulse number Pb, which is a variable and is counted fromthe burst lead, to Pb=1 (step S113). Then, the processing shifts to theburst lead control processing in step S116. If the trigger wait time Tis not larger than the burst start threshold Tth (step S112, No), theburst pulse number Pb may be incremented to be Pb+1 (step S114).Further, it may be determined whether or not the burst pulse number Pbis equal to or smaller than a predetermined burst lead control pulsenumber m (step S115). The burst lead control pulse number m may be thenumber of pulses subject to the burst lead control processing. If theburst pulse number Pb is equal to or smaller than a burst lead controlpulse number m (S115, Yes), the processing may shift to step S116, inwhich the burst lead control processing may be performed. If the burstpulse number Pb is larger than the burst lead control pulse number m(S115, No), the feedback control processing may be performed (stepS117). Then, after the burst lead control processing in step S116 or thefeedback control processing in step S117 is performed, the processingmay return to step S102.

As shown in FIG. 6, in the burst lead control processing in step S116,control amount read-out processing may first be performed (step S201).This control amount may be an EUV pulse energy control amount of theorder corresponding to a burst pulse number Pb within the learningcontrol region E1, and may be stored updatably in the control amountstorage unit 23 by the energy control processing unit 20. In the firstembodiment, this control amount may be determined based on an averagedoutput of the EUV pulse energy within the predetermined period Tw andthe value of the burst pulse number Pb, and may be held in a relationtable. Further, in step S201, the control amount read-out processing maybe performed, in which the control amount of the EUV pulse energycorresponding to the averaged output at a given time tm0 is read outwith reference to this relation table.

As shown in FIG. 10, in this control amount read-out processing, EUVpulse energy E for a count value of the number of pulses (the number ofEUV pulses) within the predetermined time Tw obtained based on thehistory in the pulse history unit 21 may be added and an averagedoutput, in which the sum is divided by the predetermined time Tw, may becalculated (step S301). The averaged output W may be a parameter log,and may be calculated with the following Expression (1).

W=(ΣE)/Tw  (1)

If the predetermined time Tw is not obtained by the time tm0, it ispreferable that EUV pulse energy for a count value of the number ofpulses by the time tm0 may be added and an averaged output obtained bydividing the sum by a time by the time tm0 may be calculated as theaveraged output W. However, the averaged output W may be directlycalculated based on Expression (1).

Then, based on the calculated averaged output W and the value of theburst pulse number Pb, the corresponding control amount may be read outfrom the control amount storage unit 23 (step S302), and the processingmay return to step S201.

For example, in the relation table stored in the control amount storageunit 23, in its initial state, control amounts preset for each EUVpulses up to the m-th pulse from the lead of the burst light emissionwithin the range of averaged outputs W divided into n stages may bestored in a matrix, as shown in a relation table Ta in FIG. 10. Forexample, if a value of an averaged value W is within the range of “W₁ toW₂” for the lead EUV pulse (burst pulse number Pb=1), the control amountC_((2,1)) may be read out.

Referring again to FIG. 6, the energy control processing unit 20 mayoutput an EUV pulse energy control signal S3 indicating the read-outcontrol amount to the driver laser 1, and the CO₂ pulsed laser beam L1may be outputted to have the EUV pulsed light emitted (step S202).

Subsequently, the energy control processing unit 20 detects the emittedEUV pulse energy based on the EUV pulse energy detection signal S2 (stepS203), and updates the history in the pulse history unit 21 based on thedetected EUV pulse energy (step S204). Then, control amount updateprocessing for updating the relation table Ta in the control amountstorage unit 23 may be performed based on the updated history in thepulse history unit 21 (step S205).

As shown in FIG. 11, in the control amount update processing, the energycontrol processing unit 20 may first calculate a difference ΔE betweenan EUV pulse energy Es detected in step S203 and a desirable EUV pulseenergy Et (step S311).

Then, to reduce the difference ΔE, the energy control processing unit 20may calculate an optimal control amount C_(new) as indicated byExpression (2) given below (step S312). C_(new) may be calculated withExpression (2).

C _(new) =C+ΔE*dC/dE*Gain  (2)

Then, the energy control processing unit 20 may update, to thecalculated control amount C_(new), a corresponding control amount C inthe control amount storage unit 23 (step S313), and the processing mayreturn to step S205. For example, if the value of the averaged output Was the parameter log is in “W₁ to W₂,” and the pulse is the lead EUVpulse (burst pulse number Pb=1), the control amount C_((2,1)) in therelation table Ta may be updated to the optimal control amount C_(new).

Referring back to FIG. 6, the energy control processing unit 20 mayreset the trigger wait time T timed by the timer 22 to T=0 (step S206),and the processing may return to step S116.

As shown in FIG. 8, in this burst lead control processing, based on theaveraged output W, which is the parameter log for the EUV pulse energywithin the predetermined time Tw, the optimal control amount for the EUVpulse energy corresponding to the averaged output W may be selected forthe each EUV pulse within the learning control region E1, and an EUVpulse may be emitted. Further, in the burst lead control processing, theenergy control processing unit 20 may calculate such optimal controlamount that would reduce the difference ΔE between a predeterminedemitted EUV pulse energy Es and the desirable EUV pulse energy Et toupdate the control amount, and the energy control processing unit 20 maylearn so that the EUV pulse, which should emit light when the averagedoutput W is in the same range, may be at the desirable EUV pulse energyEt.

Next, the feedback control processing in step S117 shown in FIG. 5 willbe described with reference to the drawings. As shown in FIG. 7, theenergy control processing unit 20 may first read out the control amountcalculated based on the immediately preceding EUV pulse energy from thecontrol amount storage unit 23 (step S211). Then, the energy controlprocessing unit 20 may output the EUV pulse energy control signal S3indicating the read-out control amount to the driver laser 1, to causethe CO₂ pulsed laser beam L1 to be oscillated and to have the EUV pulsedlight emitted (step S212).

Then, the energy control processing unit 20 may detect the emitted EUVpulse energy based on the EUV pulse energy detection signal S2 (stepS213), calculate a control amount based on the detected EUV pulse energy(step S214), and store the calculated control amount in the controlamount storage unit 23.

Then, the energy control processing unit 20 may reset the trigger waittime T timed by the timer 22 to T=(step S215), and the processing mayreturn to step S117.

As described above, in this feedback control processing, the output ofthe EUV pulse energy may be controlled so that the difference betweenthe immediately preceding EUV pulse energy and the predetermined EUVpulse energy is reduced. To be more specific, as shown in FIG. 8, theprocessing may be performed for the EUV pulses within a feedback controlregion E2.

The history held in the pulse history unit 21 may be a time history ofEUV pulse energy detection signals S2, as shown in FIG. 8( e). Thehistory held in the pulse history unit 21 may be a time history from thetime tm0 to the start of the predetermined time Tw, and the historybefore then may successively be deleted.

The averaged output W calculated in step S301 is a time average;however, since the predetermined time Tw is preset, the calculated valuemay not be divided by the predetermined time Tw, and an integrated valueof EUV pulse energy within the predetermined time Tw may be used.Alternatively, an averaged value of EUV pulse energy may be used.Further, the number of EUV pulses may serve as the parameter log.

In the first embodiment, the configuration is such that the energycontrol processing unit 20 performs the energy control for one or morelead-side pulse energy including at least the first pulse of EUV pulsesto be emitted subsequently based on the parameter log of the immediatelypreceding burst light emission, lead-side pulse energy at burst lightemission can stably be controlled at a desirable value.

Second Embodiment

In the second embodiment, the burst lead control pulse number m maybe 1. This is because the EUV pulse of the burst lead may vary largelyfrom the value of the desirable EUV pulse energy according to theparameter log. FIG. 12 shows a relation table Tb stored in the controlamount storage unit 23 in this case. In the relation table Tb, a controlamount corresponding to a range of an averaged output W may be storedand updated only for an EUV pulse of a burst lead Accordingly, thefeedback control processing in step S117 may be performed for the secondand the subsequent EUV pulses counted from the burst lead.

Third Embodiment

In the above-described first embodiment, the configuration is such thatthe control amount is read out using the relation table stored in thecontrol amount storage unit 23, and the control amount is updated;however, in the third embodiment, the configuration may be such that theburst lead control processing is performed by having the control amountread out using a relational expression indicative of the control amountcorresponding to an averaged output W and having the control amountupdated.

FIG. 13 is a flowchart showing control amount read-out processingprocedure in the burst lead control processing according to the thirdembodiment. Also, FIG. 14 is a flowchart showing the control amountupdate processing procedure in the burst lead control processingaccording to the third embodiment.

In the control amount read-out processing shown in FIG. 13, similarly tostep S301, an averaged output W may be calculated as a parameter log(step S401). Then, the obtained averaged output W may be applied to therelational expression indicated by Expression (3) for the control amountC with the averaged output W serving as a variable, whereby the controlamount may be calculated (step S402), and the processing may return tostep S201.

C=(dC/dW)*(A/exp(B×W)+D)  (3)

In Expression (3), A and B are constants, and D is an offset amount. Therelational expression for the control amount C may be set for each EUVpulse from the lead within the learning control region E1. In otherwords, the relational expressions may be set for the number of pulsescorresponding to the burst lead control pulse number m.

Also, in the control amount update processing shown in FIG. 14,similarly to step S311, the difference ΔE between the detected EUV pulseenergy Es and the desirable EUV pulse energy Et may be calculated (stepS411). Then, an optimal offset amount D_(new) for reducing thedifference ΔE may be calculated using the following Expression (4) (stepS412).

D _(new) =D+ΔE*dC/dE*Gain  (4)

Then, an offset amount D in the relational expression may be updated tothe calculated optimal offset amount D_(new) (step S413), and theprocessing may return to step S205.

Fourth Embodiment

In the above-described first embodiment, the configuration is such thatthe control amount is read out using the averaged output W within thepredetermined time Tw as the parameter log and the control amount isupdated, whereby the burst lead control processing is performed;however, in the fourth embodiment, the configuration may be such that acontrol amount is read out using the immediately preceding burst-lengthtime TB shown in FIG. 8 as the parameter log and the control amount isupdated. In other words, in the fourth embodiment, when the burst lightemission is performed, the burst-length time TB of the immediatelypreceding burst light emission that may affect the burst light emissionto be controlled may be used as the parameter log.

FIG. 15 is a flowchart showing the control amount read-out processingprocedure in the burst lead control processing according to the fourthembodiment. FIG. 16 is a flowchart showing the control amount updateprocessing procedure in the burst lead control processing according tothe fourth embodiment.

In the control amount read-out processing shown in FIG. 15, theimmediately preceding burst-length time TB may be acquired from thehistory in the pulse history unit (step S501). Then, based on the valueof the acquired burst-length time TB, the corresponding control amountmay be read out from a relation table Tc stored in the control amountstorage unit 23 (step S502), and the processing may return to step S201.

Here, in the relation table Tc, control amounts C₁, C₂, . . . , C_(n-1),C_(n) may be set respectively, for example, for an n number of ranges (0to T₁, T₁ to T₂, . . . , T_(n-1) to T_(n)) of the burst-length time TBfor the burst lead pulses. Then, for example, if the acquiredburst-length time TB is within the range of T₁ to T₂, the control amountC₂ may be read out.

Further, in the control amount update processing shown in FIG. 16,similarly to step S311, the difference ΔE between the detected EUV pulseenergy Es and the desirable EUV pulse energy Et may be calculated (stepS511). Then, to reduce the difference ΔE, an optimal control amount Cmay be calculated using the difference ΔE with Expression (2) (stepS512).

The corresponding control amount C may be updated to the calculatedoptimal control amount C_(new) (step S513), and the processing mayreturn to step S205. For example, when the optimal control amountC_(new) corresponding to the control amount C₂ is calculated,overwriting processing for updating the control amount C₂ to the optimalcontrol amount C_(new) may be performed.

Fifth Embodiment

In the above-described first embodiment, the configuration is such thatthe control amount is read out using the averaged output W within thepredetermined time Tw as the parameter log and the control amount isupdated, whereby the burst lead control processing is performed. In thefifth embodiment, the configuration may be such that the control amountis read out using the immediately preceding burst-rest time Tr shown inFIG. 8 as the parameter log, and the controlled amount is updated. Inother words, in the fifth embodiment, when the burst light emission isperformed, the burst-rest time Tr, which is a light emission rest timesince the completion of the immediately preceding burst light emissionthat may affect the burst light emission to be controlled, may be usedas the parameter log.

FIG. 17 is a flowchart showing the control amount read-out processingprocedure in the burst lead control processing according to the fifthembodiment. FIG. 18 is a flowchart showing the control amount updateprocessing procedure in the burst lead control processing according tothe fifth embodiment.

In the control amount read-out processing shown in FIG. 17, theimmediately preceding burst-rest time Tr may first be acquired from thehistory in the pulse history unit 21 (step S601). Then, based on thevalue of the acquired burst-rest time Tr, the corresponding controlamount may be read out from a relation table Td stored in the controlamount storage unit 23 (step S602), and the processing may return tostep S201.

In the relation table Td, control amounts C₁, C₂, . . . , C_(n-1), C_(n)may be set respectively, for example, for an n number of ranges (0 toTr₁, Tr₁ to Tr₂, . . . , Tr_(n-1) to Tr_(n)) of the burst-rest time Trfor the burst lead pulses. Then, for example, if the acquired burst-resttime Tr is within the range of Tr₁ to Tr₂, the control amount C₂ may beread out.

Also, in the control amount update processing shown in FIG. 18,similarly to step S311, the difference ΔE between the detected EUV pulseenergy Es and the desirable EUV pulse energy Et may be calculated (stepS611). Then, to reduce the difference ΔE, an optimal control amountC_(new) may be calculated using the difference ΔE with Expression (2)(step S612).

Then, the corresponding control amount C may be updated to thecalculated optimal control amount C_(new) (step S613), and theprocessing may return to step S205. For example, if the optimal controlamount C_(new) corresponding to the control amount C₂ is calculated,overwriting processing for updating the control amount C₂ to the optimalcontrol amount C_(new) may be performed.

Sixth Embodiment

In the above-described fourth embodiment, the configuration is such thatthe control amount is read out from the relation table Tc using theimmediately preceding burst-length time TB as the parameter log and thecontrol amount is updated. In the sixth embodiment, instead of therelation table Tc, similarly to the third embodiment, the configurationmay be such that the control amount may be read out using the relationalexpression indicative of the control amount corresponding to theimmediately preceding burst-length time TB, and the control amount maybe updated.

FIG. 19 is a flowchart showing the control amount read-out processingprocedure in the burst lead control processing according to the sixthembodiment. FIG. 20 is a flowchart showing the control amount updateprocessing procedure in the burst lead control processing according tothe sixth embodiment.

In the control amount read-out processing shown in FIG. 19, theimmediately preceding burst-length time TB may be acquired from thehistory in the pulse history unit (step S701). Then, the acquiredburst-length time TB may be inputted to a relational expressionindicative of the relationship of the control amount with respect to theburst-length time TB, the relational expression being shown inExpression (5) stored in the control amount storage unit 23; thecorresponding control amount may be calculated (step S702); and theprocessing may return to step S201.

C=(dC/dT)*(A/exp(B×TB)+D)  (5)

In Expression (5), A and B are constants, and D is an offset amount. Therelational expression for the control amount C may be set for each EUVpulse from the lead within the learning control region E1. In otherwords, the relational expressions may be set for the number of pulsescorresponding to the burst lead control pulse number m.

Also, in the control amount update processing shown in FIG. 20,similarly to step S311, the difference ΔE between the detected EUV pulseenergy Es and the desirable EUV pulse energy Et may be calculated (stepS711). Then, the optimal offset amount D_(new) for reducing thedifference ΔE may be calculated with Expression (4) (step S712). Then,the offset amount D in the relational expression may be updated to thecalculated optimal offset amount D_(new) (step S713), and the processingmay return to step S205.

In the sixth embodiment, the configuration is such that the controlamount is obtained based on the relational expression using theburst-length time TB as the parameter log; however, the configurationmay be such that the control amount may be obtained with a relationalexpression using the burst-rest time Tr, instead of the burst-lengthtime TB, as the parameter log.

Seventh Embodiment

In the seventh embodiment, the configuration may be such that a controlamount is read out from a relation table Te for control amounts setbased on a matrix of the averaged output W and the burst-length time TB,with the averaged output W within the predetermined time Tw and theburst-length time TB being used as the parameter logs, and the controlamount is updated, whereby burst lead control processing is performed.If the burst lead control pulse number m is plural, a plurality ofrelation tables may be used.

FIG. 21 is a flowchart showing the control amount read-out processingprocedure in the burst lead control processing according to the seventhembodiment. FIG. 22 is a flowchart showing the control amount updateprocessing procedure in the burst lead control processing according tothe seventh embodiment.

In the control amount read-out processing shown in FIG. 21, the averagedoutput W and the immediately preceding burst-length time TB may beacquired from the history in the pulse history unit 21 (step S801).Then, the corresponding control amount may be read out from the relationtable Te stored in the control amount storage unit 23, based on theacquired averaged output W and the burst-length time TB (step S802), andthe processing may return to step S201.

Further, in the control amount update processing shown in FIG. 22, thedifference ΔE between the detected EUV pulse energy Es and the desirableEUV pulse energy Et may be calculated (step S811). Then, to reduce thedifference ΔE, an optimal control amount C_(new) may be calculated usingthe difference ΔE with Expression (2) (step S812).

Then, the corresponding control amount C may be updated to thecalculated optimal control amount C_(new) (step S813), and theprocessing may return to step S205. For example, if the value of thecontrol amount C set when the value of the averaged output W is withinthe range of W₁ to W₂ and the value of the burst-length time TB withinthe range of T₁ to T₂ is C_((2,2)), when an optimal control amountC_(new) corresponding to this control amount C_((2,2)) is calculated,overwriting processing for updating the control amount C_((2,2)) to theoptimal control amount C_(new) may be performed.

If a control amount is calculated using a relational expression insteadof a relation table, this relational expression may be a function inwhich the control amount C is determined with the averaged output W andthe burst-length time TB being used as variables. If the burst leadcontrol pulse number m is plural, a plurality of relation tables may beused. The burst-rest time Tr may be used instead of the burst-lengthtime TB, or a relation table of a three-dimensional matrix with theburst-rest time Tr added or a function in which a control amount C isdetermined by a relational expression determined by three variablesincluding the averaged output W, the burst-length time TB, and theburst-rest time Tr may be used.

In these first through seventh embodiments, the configuration is suchthat the control amount C of at least a single lead-side EUV pulsedetermined by one of the averaged output W of the EUV pulse energywithin the predetermined time Tw, the burst-length time TB, and theburst-rest time Tr or a combination of at least two of these may be readout and updated, and the burst lead control processing is performed inwhich the learning control is performed for the at least singlelead-side EUV pulse energy to be burst-emitted next. Accordingly, thevalue of the lead-side EUV pulse energy does not become a value largelydeviated from the desirable EUV pulse energy, and stable burst lightemission can be performed.

In the above-described first through seventh embodiments, theconfiguration is such that the trigger signal S1 is indicated on eachpulse in burst light emission. In contrast, as shown in FIGS. 23 and 24,a trigger signal S1 a indicated on each burst may be used instead of thetrigger signal S1 from the exposure apparatus 100. In this case, theenergy control processing unit 20 may be configured to generate an EUVpulse energy control signal S3 based on rising timing of the triggersignal S1 a. A repetition rate within the burst of the EUV pulse energycontrol signal S3 may be held in the EUV light source controller C inadvance or may be designated by the exposure apparatus 100. Thegenerated EUV pulse energy control signal S3 may be inputted to thedriver laser 1 and to the pulse history unit 21 and the timer 22 aswell. The pulse history unit 21 may treat the EUV pulse energy controlsignal S3 as the trigger signal S1 and may save the history of the EUVpulse energy. Also, the timer 22 may treat the EUV pulse energy controlsignal S3 as the trigger signal S1 and may perform timing processing. Inother words, even with the trigger signal S1 a indicative of each burstlight emission period, as long as the energy control processing unit 20generates EUV pulse energy control signals S3 corresponding to secondand later trigger signals S1 a (or first and later trigger signals S1a), processing similar to any of the above-described first throughseventh embodiments can be performed.

First Modification

In the first modification, a detailed control configuration of a driverlaser 1 that is controlled by the EUV light source controller Caccording to any of the above-described first through seventhembodiments will be described. As shown in FIG. 25, the driver laser 1may include an oscillator 25 including a master oscillator MO such as asemiconductor laser that oscillates a longitudinal-mode pulsed laserbeam in gain bandwidths of a preamplifier PA and a main amplifier MA,and the preamplifier PA and the main amplifier MA that successivelyamplify the pulsed laser beam outputted from the oscillator 25. Also,the driver laser 1 may include a driver laser controller C1. The driverlaser controller C1 may output to the oscillator 25 a trigger signal S11and a laser pulse energy control signal S13 that control the oscillationof the CO₂ pulsed laser beam L1 from the oscillator 25, based on atrigger signal S1 and an EUV pulse energy control signal S3 outputtedfrom an EUV light source controller C.

The preamplifier PA may be a slab amplifier. The laser beam outputtedfrom the oscillator 25 may be incident on an input window of thepreamplifier PA. The preamplifier PA may include an amplificationregion, amplify the inputted laser beam through multipass-amplificationwith mirrors M31 and M32 in the amplification region, and output theamplified laser beam through an output window toward an HR (highreflection) mirror M11. In this way, the single longitudinal-mode pulsedlaser beam may pass through the amplification region filled with a gainmedium within the preamplifier PA to be further amplified efficiently,and be outputted therefrom.

The amplified pulsed laser beam outputted from the preamplifier PA maybe reflected by the HR mirrors M11 and M12, and may enter a relayoptical system R2. The relay optical system R2 may expand a beam widthor diameter of the amplified pulsed laser beam so that the amplifiedpulsed laser beam enters an amplification region of the main amplifierMA filled with mixed gas serving as a gain medium for the CO₂ laser beamso as to have the space filled with the amplified pulsed laser beam.With this, the amplified pulsed laser beam may pass through theamplification region filled with the gain medium within the mainamplifier MA to be further amplified efficiently, and be outputted.

Then, the amplified pulsed laser beam outputted from the main amplifierMA may be collimated by a relay optical system R3. The collimated laserbeam may be reflected with high reflectivity by the HR mirror M1 and theoff-axis paraboloidal mirror M2, and may enter the EUV chamber 10 of theEUV light generation apparatus 2 through the window 15.

Here, an optical element M21, which is configured of a partialreflection mirror or a beam splitter for detecting the output of the CO₂pulsed laser beam L1, may be provided between the HR mirror M1 and theoff-axis paraboloidal mirror M2. The laser beam reflected by the opticalelement M21 may be focused by a focusing lens R21, and thereafter theoutput of the CO₂ pulsed laser beam L1 may be detected by a laser beamdetector 24. The pulse energy of the CO₂ pulsed laser beam L1 detectedby the laser beam detector 24 may be inputted as a laser pulse energydetection signal S5 to the EUV light source controller C and to thedriver laser 1.

The driver laser controller C1 may output a trigger signal S11 and alaser pulse energy control signal S13 to the oscillator 25, and thusperform energy control for the pulsed laser beam to be inputted into thepreamplifier PA. At this time, the driver laser controller C1 maycontrol the driver laser 1 based on the inputted laser pulse energydetection signal S5. The control for the EUV pulse energy outputted fromthe EUV light generation apparatus 2 may be performed by the high-orderEUV light source controller C.

That is, in the first modification, the configuration may be such thatoscillation timing, an oscillation wavelength, and an oscillationwaveform of the pulsed laser beam inputted to the preamplifier PA arecontrolled.

As shown in FIG. 26, the master oscillator MO, for example, may beconfigured such that a Pockels cell 34, a polarizer 35, and a CO₂ gainmedium 33 are arranged between a pair of resonator mirrors 31 and 32 inthat order from the resonator mirror 31 side. The CO₂ gain medium 33 maybe excited in a predetermined state with voltage of a constant frequencybeing applied from a laser power supply 37. The polarizer 35, forexample, may transmit P-polarized component of a laser beam with respectthereto. A Pockels cell control power supply 36 may output to thePockels cell an oscillation control signal S30 for generating apredetermined pulse shape at predetermined timing based on the triggersignal S11 and the laser pulse energy control signal S13. The Pockelscell 34 with voltage being applied thereto may rotate the polarizationof the laser beam incident thereon while predetermined voltage or higheris applied thereto. First, in a state in which voltage is not applied tothe Pockels cell 34 based on the oscillation control signal S30, thelinearly polarized CO₂ laser beam is transmitted through the Pockelscell 34 without having the polarization thereof rotated; thus, the CO₂laser beam is incident on the polarizer 35 as the P-polarized componentand is not outputted toward the preamplifier PA. Here, whenpredetermined or higher voltage is applied to the Pockels cell 34 for apredetermined period based on the oscillation control signal S30, theamplified CO₂ laser beam incident on the Pockels cell 34 may beconverted to a laser beam of S-polarized component with respect to thepolarizer 35 by the Pockels cell 34, and be reflected by the polarizer35 to be outputted toward the preamplifier PA. The laser pulse energyoutputted from the polarizer 35 toward the preamplifier PA may becontrolled by adjusting the length of the predetermined period duringwhich voltage is applied by the Pockels cell control power supply 36.

In the oscillator shown in FIG. 26, the configuration is such that thelaser pulse energy is controlled by controlling the predetermined periodduring which the voltage is applied from the Pockels cell control powersupply 36 to the Pockels cell 34. In contrast, as shown in FIG. 27, thePockels cell control power supply 36 may apply to the Pockels cell 34 acontrol signal S31 for applying voltage for a predetermined period basedonly on the trigger signal S11, and the laser power supply 37 may outputa voltage control signal S32 for controlling the excited state of theCO₂ gain medium 33 based on the pulse energy control signal S13 inputtedto the laser power supply 37. As a result, the laser pulse energyoutputted from the polarizer 35 toward the preamplifier PA may becontrolled.

Also, as shown in FIG. 28, a semiconductor laser may be used as themaster oscillator MO. The semiconductor laser may preferably be aquantum-cascade laser. An output coupling mirror 42 may be provided atthe front side of the master oscillator MO, and a rear optical module 43may be provided at the rear side. The output coupling mirror 42 and therear optical module 43 may form an optical resonator with asemiconductor device 41 having an optical amplification region arrangedtherebetween. This optical resonator may be controlled by asemiconductor laser controller C2. The semiconductor laser controller C2may output an oscillation wavelength signal S41 to a longitudinal-modecontrol actuator 45 through a longitudinal-mode controller 44. Thislongitudinal-mode control actuator 45 may control a wavelength of alaser beam outputted from the optical resonator. Also, the semiconductorlaser controller C2 may output an oscillation pulse shape signal S42 toa current control actuator 46 based on the trigger signal S11 and thelaser pulse energy control signal S13. This current control actuator 46may control a current waveform that is applied to the semiconductordevice 41, and may control a pulse shape of the pulsed laser beamoutputted from the optical resonator and the timing at which the pulsedlaser beam is outputted. This pulsed laser beam of which the pulse shapeand the output timing are controlled may be inputted to the preamplifierPA. The pulse shape may include a pulse width and a pulse peak value,and hence by controlling the pulse shape, the pulse energy can becontrolled.

It is to be noted that the output coupling mirror 42 may be a mirrortreated with partial reflection mirror coating. The output couplingmirror 42 may output a laser beam, and may also return part of the laserbeam into the optical resonator for resonant amplification. The rearoptical module 43 may include a collimator lens and a grating with theLittrow arrangement for selecting a predetermined wavelength of thelaser beam. The laser beam outputted from the rear side of thesemiconductor device 41 is collimated by the collimator lens, andoutputted as a collimated beam toward the grating, and the laser beamthe wavelength of which is selected by the grating is returned to thesemiconductor device 41 through the collimator lens. With this, thedesirable single longitudinal-mode laser beam can be outputted from theoutput coupling mirror 42 toward the preamplifier PA.

Further, in the above-described first modification, the laser pulseenergy is controlled by having the master oscillator MO beingcontrolled; however, the configuration may be such that the laser pulseenergy inputted to the preamplifier PA may be controlled in theoscillator 25 but outside the master oscillator MO. In this case, alaser beam with predetermined laser pulse energy may be outputted fromthe master oscillator MO.

For example, as shown in FIG. 29, the Pockels cell 34 and the polarizer35 shown in FIG. 26 may be provided outside the master oscillator MO. Inparticular, the Pockels cell 34 and the polarizer 35 may be providedoutside the front-side resonator mirror 31 and 32 in that order towardthe preamplifier PA. The Pockels cell control power supply 36 may causethe Pockels cell 34 to function as a shutter by controlling the voltageapplied to the Pockels cell 34, and may control the laser pulse energyoutputted from the master oscillator MO by controlling duration anddegree of opening of the shutter.

Also, as shown in FIG. 30, the Pockels cell control power supply 36 mayapply voltage, which causes the Pockels cell 34 to be open, for apredetermined period and the voltage applied from the laser power supply37 to the CO₂ gain medium 33 may be controlled, whereby the intensity ofthe laser beam outputted from the master oscillator MO may becontrolled.

Second Modification

In the above-described first modification, the configuration is suchthat the laser pulse energy inputted to the preamplifier PA iscontrolled by controlling the oscillator 25. In contrast, in the secondmodification, a regenerative amplifier 50 may be provided between theoscillator 25 and the preamplifier PA. The driver laser controller C1may control the regenerative amplifier 50, and hence the laser pulseenergy of the laser beam inputted to the preamplifier PA may becontrolled. If the regenerative amplifier 50 is used, a pulsed laserbeam with a small output such as a laser beam outputted from asemiconductor laser can efficiently be amplified in a state in which thepulse shape thereof is maintained, and be outputted to the preamplifierPA. The pulsed laser beam outputted from the regenerative amplifier 50may efficiently be amplified by the preamplifier PA and the mainamplifier MA.

The regenerative amplifier 50 may amplify a seed pulsed beam SAoutputted from the oscillator 25, and output the seed pulsed beam SA tothe preamplifier PA. In the regenerative amplifier 50, for example, asshown in FIG. 31, a Pockels cell 53, a polarizer 58, a CO₂ laseramplification unit EA, a Pockels cell 54, and a quarter waveplate 57 maybe arranged between a pair of resonator mirrors 51 and 52 in that orderfrom the resonator mirror 51 side. The seed pulsed beam SA outputtedfrom the oscillator 25 may be made to enter the regenerative amplifier50 through the polarizer 58, and the seed pulsed beam SA may bereciprocated between the resonator mirrors 51 and 52 to be amplified,and outputted as an amplified pulsed laser beam SB to the preamplifierPA through the polarizer 58.

Now, the operation of the regenerative amplifier 50 will be describedwith reference to a timing chart shown in FIG. 32. The pulsed laser beamoutputted from the oscillator 25 may be incident on the polarizer 58 asthe seed pulsed beam SA at timing t0, for example. The S-polarizedcomponent of this incident beam, for example, may be reflected by thepolarizer 58 and introduced into a resonator in the regenerativeamplifier 50. The laser beam introduced into the regenerative amplifier50 may be amplified as it passes through an amplification region of theCO₂ laser amplification unit EA, transmitted through the Pockels cell54, to which voltage is not applied, without a phase shift, converted toa circularly polarized laser beam as it is transmitted through thequarter waveplate 57, reflected with high reflectivity by the resonatormirror 52, and converted to a linearly polarized laser beam that wouldbe incident on the polarizer 58 as the P-polarized component. This laserbeam may further be amplified as it passes through the amplificationregion of the CO₂ laser amplification unit EA. The amplified laser beammay be incident on the polarizer 58 as a laser beam of the P-polarizedcomponent, transmitted through the polarizer 58, transmitted through thePockels cell 53, to which voltage is not applied, without a phase shift,and reflected with high reflectivity by the resonator mirror 51. Thelaser beam reflected with high reflectivity may be transmitted againthrough the Pockels cell 53 without a phase shift, transmitted throughthe polarizer 58, and further amplified as it passes again through theamplification region of the CO₂ laser amplification unit EA.

Then, the voltage is applied to the Pockels cell 54 at timing t1, thephase of the laser beam may change by a quarter wavelength as it passesthrough the Pockels cell 54, whereby the laser beam may be converted toa circularly polarized laser beam. The circularly polarized laser beammay be transmitted through the quarter waveplate 57, whereby it isconverted to a linearly polarized laser beam that would be incident onthe polarizer 58 as the S-polarized component. The laser beam reflectedby the resonator mirror 52 may be converted into the circularlypolarized laser beam as it is transmitted again through the quarterwaveplate 57. Thereafter, the laser beam may be converted into alinearly polarized laser beam that would be incident on the polarizer 58as the P-polarized component as it is transmitted through the Pockelscell 54 to which voltage is applied. The laser beam may further beamplified as it passes through the amplification region of the CO₂ laseramplification unit EA, transmitted through the polarizer 58, transmittedthrough the Pockels cell 53 to which the voltage is applied without aphase shift, reflected with high reflectivity by the resonator mirror51, transmitted again through the Pockels cell 53 to which the voltageis not applied, and transmitted through the polarizer 58. In the statein which voltage is applied to the Pockels cell 54, the laser beam maybe amplified as it is reciprocated between the resonator mirrors 51 and52.

The voltage may be applied to the Pockels cell 53 at timing t2 at whichthe amplified pulsed laser beam SB is outputted outside, and the laserbeam may be converted into the circularly polarized laser beam as it istransmitted through the Pockels cell 53 to which the voltage is notapplied. The circularly polarized laser beam may be reflected with highreflectivity by the resonator mirror 51, and converted into a linearlypolarized laser beam which would be incident on the polarizer 58 as theS-polarized component as it is transmitted again through the Pockelscell 53 to which the voltage is applied. The laser beam may be reflectedwith high reflectivity by the polarizer 58, and outputted as theamplified pulsed laser beam SB toward the external preamplifier PA.

Here, for the Pockels cells 53 and 54 of the regenerative amplifier 50,ON and OFF of voltage application may be performed by Pockels cellcontrol power supplies 55 and 56. A regenerative amplifier controller C3may control the Pockels cell control power supplies 55 and as describedabove based on the laser pulse energy control signal S13. That is, thelaser pulse energy of the amplified pulsed laser beam SB can becontrolled by increasing or decreasing the period during which voltageis applied to the Pockels cell 54. It is to be noted that the triggersignal S11 may be inputted to the semiconductor laser controller C2, andhence timing at which the seed pulsed beam SA is oscillated may becontrolled.

Third Modification

In the above-described first modification, the oscillator 25 iscontrolled. In the second modification, the laser pulse energy iscontrolled by controlling the regenerative amplifier 50. In contrast, inthe third modification, the laser pulse energy may be controlled bycontrolling at least one of the preamplifier PA and the main amplifierMA.

In particular, as shown in FIG. 33, the driver laser controller C1 mayoutput a laser pulse energy control signal S14 to an amplifier powersupply controller 60 that controls a preamplifier power supply 61, whichis a laser power supply for the preamplifier PA, and a main amplifierpower supply 62, which is a laser power supply for the main amplifierMA. The amplifier controller 60 performs the laser pulse energy controlby controlling the excitation intensity of the preamplifier PA and themain amplifier MA based on the laser pulse energy control signal S14.

Also, as shown in FIG. 34, in the case where a pre-pulse laser 101 isused for irradiating the target 13 with pre-pulsed laser beam before thetarget 13 is irradiated with the CO₂ pulsed laser beam L1, theconfiguration may be such that EUV pulse energy may be controlled bycontrolling laser pulse energy of the laser beam outputted from thepre-pulse laser 101. If the pre-pulsed laser beam is used, when thetarget 13 is irradiated with the CO₂ pulsed laser beam L1, the target 13may be turned into plasma more efficiently, whereby the EUV pulsed lightcan efficiently be emitted.

The pre-pulsed laser beam may strike the target 13 via an off-axisparaboloidal mirror M102. An optical element M121 configured of apartial reflection mirror or a beam splitter may be provided at theupstream side of the off-axis paraboloidal mirror M102. The pre-pulsedlaser beam may be incident on a pre-pulsed laser beam detector 121through the optical element M121 and a focusing lens R121, and thepre-pulsed laser beam detector 121 may detect the pulse energy of thepre-pulsed laser beam, and output a pre-pulsed laser pulse energydetection signal S6 to the pre-pulse laser 101 and the EUV light sourcecontroller C. The EUV light source controller C may output a controlsignal S60 to the pre-pulse laser 101 and control the laser pulseenergy.

It is to be noted that the laser pulse energy of only the pre-pulselaser 101 may be controlled. Alternatively, the laser pulse energy ofboth the pre-pulse laser 101 and the driver laser 1 may be controlled.

The above-described embodiments and the modifications thereof are merelyexamples for embodying this disclosure, and this disclosure is notlimited thereto. Making various modifications according to thespecifications or the like is within the scope of this disclosure, andit is apparent from the above description that other various embodimentscan be made within the scope of the disclosure. For example, it isneedless to mention that the modifications indicated for each embodimentmay be applied to another embodiment as well.

1. An extreme ultraviolet light generation apparatus, comprising: alaser apparatus; a chamber provided with an inlet for introducing alaser beam outputted from the laser apparatus to the inside thereof; atarget supply unit provided to the chamber for supplying a targetmaterial to a predetermined region inside the chamber; a collectormirror disposed in the chamber for collecting extreme ultraviolet lightgenerated when the target material is irradiated with the laser beam inthe chamber; an extreme ultraviolet light detection unit for detectingenergy of the extreme ultraviolet light; and an energy control unit forcontrolling energy of the extreme ultraviolet light. 2-21. (canceled)